Methods, systems, and apparatuses for increasing efficiency in computed tomography detection

ABSTRACT

Methods, computer-readable mediums, and systems are provided. In one embodiment, a method detects at least one faulty X-ray detector signal and adjusts a conveyor speed and/or a gantry speed in accordance with the detection to increase information for image reconstruction. In another embodiment, a method detects a high volume time. Upon detection of the high volume time conveyor speed and gantry speed is increased during the high volume time. After expiration of the high volume time, the conveyor speed and gantry speed is reduced. In yet other embodiments, the computer-readable mediums and systems are also provided which perform similar features recited by the above methods.

GOVERNMENT RIGHTS IN THIS INVENTION

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of (Grant No.TSA-20-03-C-01900D089) awarded by the United States Department ofHomeland Security.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to X-ray detectorscanning and more particularly, to methods, computer-readable mediums,and systems for increasing efficiency in computed tomography (“CT”)scanning.

2. Description of the Related Art

In some known computed tomography (“CT”) imaging system configurations,an X-ray source projects a fan-shaped or a cone-shaped beam, which iscollimated to hit a linear or two dimensional array of detectors. TheX-ray beam passes through an item being imaged. The beam, after beingattenuated by the item, impinges upon an array of radiation detectors.The intensity of the attenuated radiation beam received at the detectorarray is dependent upon the attenuation of an X-ray beam by the item.Each detector element of the array produces a separate electrical signalthat is a measurement of the beam intensity at the detector location.The intensity measurements from all the detectors are acquiredseparately to produce a transmission profile.

Sometimes information from a detector will not be received forconversion into a CT image (e.g., due to a bad detector or lack oftransmission of an output signal derived from an output of thedetector(s)). Typically, when a CT image is generated using informationfrom less than the appropriate number of detectors the generated imagedoes not have the desired resolution. In an effort to acquire properresolution, the scanner is typically placed “out of service” until it isrepaired (e.g., by replacing a detector(s) in the detector array orreplacing the detector array); or an interpolation is performed whichincludes the bad detector. However, interpolation techniques are only anapproximation (“a guesstimate”) of what the information gathered by thebad detector should be and typically do not account for a significantdifference between the bad detector and adjacent detectors used in theinterpolation.

In addition, there are times when the X-ray scanner does not scan fastenough to keep up with scanning backlog. Increasing the scanning rate ofthe X-ray scanner can decrease the life of the scanner and itscomponents. For example, when the rotational velocity of the gantry isincreased there is an increase in load force placed on the gantry mainbearing. This increased rotational loading causes additional loadstress, which reduces bearing life in a disproportional manner. Inaddition, increasing the rotational rate of the gantry can also reducethe life of the charging capacitors.

When a scanner is out of service, a disruption in an ability to use thescanner creates delays and quite often a backlog of people waiting toutilize the scanner. In addition, increasing scanning rate in existingscanning systems diminishes the life of the scanner. Thus, there is aneed to diminish scanning backlog and better utilize scanner resources.

BRIEF DESCRIPTION

These and other deficiencies of the prior art are addressed byembodiments of the present invention, which generally relates to X-rayscanning systems and more particularly, to methods, computer-readablemediums, and systems that increase computed tomography (“CT”) scanning.In one embodiment, a method detects at least one faulty X-ray detectorsignal and adjusts a conveyor speed and/or a gantry speed in accordancewith the detection to increase information for image reconstruction. Inanother embodiment, a method detects a high volume time. Upon detectionof the high volume time conveyor speed and gantry speed is increasedduring the high volume time. After expiration of the high volume time,the conveyor speed and gantry speed is reduced.

Other embodiments are also provided in which computer-readable mediumsand systems perform similar features recited by the above methods.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toexemplary non-limiting embodiments, some of which are illustrated in theappended drawings.

FIG. 1 is a perspective view of a gantry/conveyor combination inaccordance with aspects of this disclosure.

FIG. 2 depicts a perspective view of an emitter and detector arraycombination in accordance with aspects of this disclosure.

FIG. 3 depicts an embodiment of a block diagram used in accordance withaspects of this disclosure.

FIG. 4 depicts an embodiment of an exemplary first method used inaccordance with aspects of this disclosure.

FIG. 5 depicts an embodiment of an exemplary second method used inaccordance with aspects of this disclosure.

FIG. 6 depicts an embodiment of an exemplary third method used inaccordance with aspects of this disclosure.

FIG. 7 depicts an embodiment of an exemplary fourth method used inaccordance with aspects of this disclosure.

FIG. 8 depicts an embodiment of an exemplary fifth method used inaccordance with aspects of this disclosure.

FIG. 9 depicts an embodiment of an area of influence of an exemplaryemitter on an exemplary detector array in accordance with aspects ofthis disclosure.

FIG. 10 depicts an embodiment of an exemplary sixth method used inaccordance with aspects of this disclosure.

FIG. 11 depicts an exemplary first graph of aspects of the invention.

FIG. 12 depicts a close up view of a portion of the exemplary firstgraph depicted in FIG. 11.

FIG. 13 depicts an exemplary graph of the CT value corresponding withthe edge of an object created aspects of this disclosure.

FIG. 14 depicts an exemplary computed tomography (“CT”) image slice at a1.5000 pitch utilizing signals from all detectors.

FIG. 15 depicts another exemplary CT image slice at a 1.5000 pitchutilizing signals from some detectors.

FIG. 16 depicts an exemplary graph 1100 in accordance with aspects ofthis disclosure.

FIG. 17 depicts an exemplary CT image slice in accordance with aspectsof the invention at a 1.5000 pitch utilizing signals from somedetectors.

FIG. 18 an embodiment of a high-level block diagram of a computerarchitecture used in accordance with aspects of the invention.

To facilitate understanding, identical reference numerals have beenused, wherever possible, to designate identical elements that are commonto the figures.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a more thorough understanding of the invention. As will beapparent to those skilled in the art, however, various changes usingdifferent configurations may be made without departing from the scope ofthe invention. In other instances, well-known features have not beendescribed in order to avoid obscuring the invention. Thus, the inventionis not considered limited to the particular illustrative embodimentsshown in the specification and all such alternate embodiments areintended to be included in the scope of the appended claims.

There are times when the rate at which items need to be scanned ishigher than usual (also known as “peak times”). Generally, as usedherein, “peak times” are broadly defined as holidays, weekends, and/orany other time span flagged as a higher volume than normal time span.Peak times can be pre-stored in memory, flagged as peak times remotely,and/or flagged as peak times on “the fly” (e.g., by an X-ray scanneroperator).

X-ray scanners occasionally fail to operate as desired. The failure canbe due to any one of a number of reasons. For example, the failure canbe due to a faulty detector(s) in the detector array (e.g., to properlyreceive and/or interpret radiation from the X-ray emitter);alternatively the failure can be due to a component not receiving anoutput signal (or a derivative signal of the output signal) from thedetector(s). Generally, as used herein, a “detector failure” is broadlydefined as an occurrence of either (or both) a failure of thedetector(s) to properly receive and/or interpret radiation from theX-ray emitter; or a failure to receive the output signal (or thederivative the of the output signal) from the detector(s). Generally, asused herein, “pitch” is broadly defined as the ratio between the amountof motion of the detector array/X-ray emitter with respect to theconveyor (e.g., the conveyor motion with respect to the gantry) thathappens during a full rotation of the gantry and the length of thedetector in the direction of motion of the conveyor. Further, asgenerally used herein, a “bad” detector is broadly defined as anydetector that malfunctions. A non-limiting example of a malfunction is afailure to receive information transmitted by the detector. In addition,“contraband,” as used herein is broadly defined as any prohibiteditem(s) (e.g., explosives, explosive devices, weapons, items which canbe used as weapons, flammable or combustible items, liquids, and/oritems exceeding a predetermined size).

When less than the desired number of detectors in the detector arrayperform (i.e., at least one of the detectors fails), the detector arrayscans at less than the desired resolution. Such decrease of resolutionmay be limited to portions or parts of the acquired data. Scanning atless than the desired resolution often renders the resultantreconstructed image unusable for its intended purpose (e.g., identifyingcontraband, identifying medical abnormalities, and the like).

Further, a resultant reconstructed image from less than the requisitenumber of computed tomography (“CT”) slices (i.e., resulting in areconstructed image having a lower resolution than desired) can alsorender the resultant reconstructed image unusable for its intendedpurpose.

Some aspects of the invention include, but are not limited to, adjustingthe speed of the conveyor; adjusting the speed of the gantry; and,adjusting the speed of the conveyor in combination with adjusting thespeed of the gantry. Aspects of the invention are described herein asutilizing an X-ray emitter/detector array combination that rotates.However, it is appreciated that aspects of the invention can be usedwith scanners that have a stationary X-ray emitter and/or detectorarray.

One of the many benefits of this disclosure is a continued operation ofthe EDS machine even though one or more detector cells is not operatingto specifications (as determined by on-board detector diagnostics). As aremediation to the problem of failed detector cells, the conveyor speedwould be decreased and/or the gantry speed would be increased. Thiswould result (in some embodiments) in the increased proximity (ordensity) of “spiral slices”. Increasing the proximity of the slices inthis way will (enabling better resolution) would be used in conjunctionwith detector signal averaging across the failed detector cell(s). Forexample the signal on each side of a bad detector signal (pixel) can beaveraged (also reduces on-screen visual artifacts). The increaseddensity of spiral scans due to slowing the conveyor means that there isless risk that the averaging of signals across adjacent detectors wouldresult in missed detection of a thin sheet of explosive having alocation relative to the conveyor and gantry might coincide preciselywith the rotational trajectory of the failed detector cell.

As disclosed herein a reduction in conveyor speed of about 30% couldenable sufficient improvement in the EDS system resolution to allowdetector signals from detectors adjacent to the failed detector(s) to beaveraged and substituted for that of a bad detector cell with minimalloss in the ability of the system to detect sheet explosives (sheetexplosives being the detection case that is perhaps most difficult tomitigate in this situation). It is further appreciated that loss ofmultiple detector cell, as long as these cells are not in closeproximity, can further be allowed in the same gantry. In variousembodiments, the mapping of the locations of these failed detector celllocations can be part of a critical failure diagnostic routine.

When at least one detector fails, the resolution of the reconstructedimage can be increased by increasing the amount of time that an itemspends within the scanning area of the X-ray emitter/detector array(i.e., increasing the amount of time that an item is in the gantry). Invarious embodiments, slowing the speed of the conveyor can increase theamount of time that an item spends in the gantry. Special algorithms maybe used to utilize correlate the speed of the gantry 104 with the speedof the conveyor 102 in such a way that there is very little or no lossof resolution when there is at least one bad detector.

In other embodiments, compensation for a failed detector(s) can beobtained by increasing the rotational speed of the gantry to increasethe number of CT slices as the conveyor moves at its normal speed. Inyet other embodiments, compensation for a failed detector(s) can beobtained by a combination of decreasing the speed of the conveyor andincreasing the rotational speed of the gantry.

FIG. 1 is a perspective view of a gantry/conveyor combination 100. Thegantry/conveyor combination 100 includes a conveyor 102 and gantry 104.The gantry 104 includes an emitter 106 (e.g., an X-ray emitter), adetector array 108, and a gantry tunnel 112. In operation, the conveyor102 moves such that when an item (e.g., item 110) is placed on conveyor102, the conveyor 102 moves the item towards; through; and past thegantry 104 and gantry tunnel 112.

The X-ray emitter 106 and the detector array 108 are rotated with thegantry 104 within the imaging plane and around the item(s) to be imagedsuch that the angle at which an X-ray beam intersects the item 110constantly changes (hereinafter each change is referred to as “a view”).As the item 110 passes through the gantry 104, the gantry 104 gathersx-ray intensity data acquired from detectors in the detector array 108for each view. Typically, each view is about 0.25 degrees apart from animmediately preceding view. Thus, for a full gantry rotation there canbe about 1440 views.

Aspects of this disclosure correlate image resolution with the speed ofthe conveyor 102 and the rotational speed of the gantry 104. Forexample, in various embodiments, when a detector(s) in the detectorarray 108 is bad, the speed of conveyor 102 is decreased and/or thespeed of the gantry 104 can be increased. When at least one detector isbad, increasing image resolution compensates for the bad detector(s).

For example in one embodiment, when it is determined that at least onedetector is bad (explained in greater detail below) the speed ofconveyor 102 is decreased (e.g., decreased below speed “x”) while thespeed of the gantry 104 remains at a normal operating speed (e.g., about120 R.P.M.s). Because an item moves slower (due to the reduced conveyorspeed) the gantry 104 has more time to rotate around the item and gathermore data on the item.

In other embodiments, when at least one bad detector is detected, thespeed of the gantry 104 is increased above its normal rotational speed(e.g., from a range of about 121 R.P.M.s up to about 150 R.P.M.s andhigher) while the speed of the conveyor 102 is maintained at theexemplary speed “x.” Due to the increased rotational speed of the gantry104, the gantry 104 acquires more data for the item and does so at afaster rate. Because more data is acquired, the reconstructed image willhave a higher resolution to compensate for the lack of information dueto the bad detector(s).

In yet other embodiments, when at least one bad detector is detected,the speed of the conveyor 102 is decreased and the rotational speed ofthe gantry 104 is increased. By decreasing the speed of the conveyor 102and increasing the rotational speed of the gantry 104, neither thedecreased conveyor speed nor the increased gantry speed have to be aslarge as in the previously described embodiments.

In still other embodiments, all of the detectors are functioning withinparameters. In these embodiments, when a time span is flagged as a “highuse” time (e.g., during a high travel time such as weekends or holidays)or there is a backlog of items to be scanned, the rotational speed ofthe gantry 104 is increased (e.g., up to about 150 R.P.M.s) and thespeed of the conveyor 102 is increased. Increasing the rotational speedof the gantry 104 increases the rate at which information is acquired.However, because all of the detectors are functioning within parametersan increase in image resolution is not necessarily required. As such,the speed of the conveyor 102 can be increased because of the increasedgantry 104 rotational speed.

FIG. 2 depicts a perspective view of an embodiment of the emitter 106and detector array 108. The emitter 106 emits X-rays that the detectorarray 108 is designed to detect. The emitter 106 and detector array 108combination is known and will not be discussed in detail. The detectorarray 108 has a plurality of detectors (e.g., thousands of detectors).For simplicity, the detector array 108 is described utilizing a few ofthe detectors (i.e., detectors 200, 202, 204, 234, 270, 282, 286, and288) in the detector array 108.

FIG. 3 depicts an embodiment of a block diagram of a system 300 used inaccordance with aspects of this disclosure. System 300 includes thegantry/conveyor combination 100, a control mechanism 304, a processor314, a user interface 322, memory 330, an image reconstruction subsystem316, a conveyor motor controller subsystem 320, the conveyor 102, and abaggage handling system 324.

The gantry/conveyor combination 100 includes the gantry 104, the emitter106, and the detector array 108. Each detector (e.g., detectors 200,202, 204, 234, 270, 282, 286, and 288) in the detector array 108produces an electrical signal that represents the intensity of animpinging X-ray beam and hence allows estimation of the attenuation ofthe beam as it passes through item 110. During a scan to acquire X-rayprojection data, gantry 104 and the components mounted thereon rotateabout a center of rotation 328.

Rotation of gantry 104, the operation of X-ray emitter 106, movement(e.g., speed control) of the conveyor 102, and a determination ofdetector failure are governed by the control mechanism 304. The controlmechanism 304 includes an X-ray controller 306 that provides power toX-ray source 106, a gantry motor controller 308 that controls therotational speed and position of gantry 104, a conveyor motor controller320, a detector signal checker 310 to check for detector failure, and adata acquisition system (“DAS”) 312. The detector signal checker 310operates as described below and depicted in subsequent figures.

The DAS 312 samples analog data from detector array 108 and converts thedata to digital signals for subsequent processing. An imagereconstructor 316 receives sampled and digitized X-ray data from DAS 312and performs high-speed image reconstruction. The reconstructed image isapplied as an input to the processor 314, which stores the image inmemory 330.

Processor 314 may also receive commands and scanning parameters from anoperator (not shown) via the user interface 322 (e.g., a cathode raytube, a keyboard, a mouse, and/or like device).

The operator can supply commands and parameters via the user interface322 to instruct the processor 314 to provide control signals andinformation to the DAS 312, the X-ray controller 306, the gantry motorcontroller 308, the conveyor motor controller 320, and the detectorsignal checker 310.

FIG. 4 depicts a high-level block diagram of an embodiment of a method400 used in accordance with aspects of this disclosure. The method 400begins at step 402 and proceeds to step 404.

At step 404, the method 400 detects a flagged time period. This flaggedperiod can be time spans which include, but are not limited to,holidays; weekends; times annotated by history as high traffic times;and/or times when items need to be scanned faster. When a flagged timeperiod is detected, the method 400 proceeds to step 406.

At step 406, the rotational speed of the gantry 104 is increased. Forexample, the gantry speed can be increased above 120 R.P.M.s (e.g., arange of about 121 R.P.M.s to about 150 R.P.M.s in various embodimentsand higher than 150 R.P.M.s in other embodiments). Because there is anincrease in the rotational rate of the gantry 104, information regardingthe various views is acquired at a faster rate. Because informationneeded to reconstruct an image is acquired at the faster rate the speedof the conveyor 102 can also be increased. For example, when asignificant number of detectors (e.g., all or almost all of thedetectors) is functioning properly, the gantry 104 can be increased toabout 150 R.P.M.s and the speed of the conveyor 102 can likewise beincreased. The speed of the gantry 104 and conveyor 102 is increasedduring the flagged time period. By increasing the speed of the gantry104 and conveyor 102 during the flagged time(s) wear and tear on thesystem 100 is lower than if the gantry 104 and conveyor 102 were alwaysrun higher speeds (e.g., at speeds higher than 120 R.P.M.s). After theexpiration of the flagged time period, the speed of the gantry 104 andconveyor 102 is reduced (e.g., to the same values prior to theoccurrence of the flagged time period). In addition, after theexpiration of the flagged time period, the method proceeds to and endsat step 408.

Method 400 also includes optional steps 410 and 412 (depicted usingdashed lines). At step 406, the method 400 optionally proceeds towardsstep 410 and/or step 412. At optional step 410, the baggage handlingsystem 324 is notified of the increase in gantry speed and conveyorspeed. At optional step 412, the operator of system 100 is notified ofthe increase in gantry speed and conveyor speed.

Although optional steps 410 and 412 are depicted as occurring after step406, in other embodiments optional steps 410 and 412 can occur afterstep 404 (i.e., prior to step 406).

FIG. 5 depicts an embodiment of a method 500 used in accordance withaspects of this disclosure. The method 500 begins at step 502 andproceeds to step 504.

At step 504, high volume is detected. An operator of system 100 candetect the high volume. High volume detection by the user allows greatercontrol over the system 100. For example, when high volume is detected,the method 500 proceeds to step 506.

At step 506, the user, in response to the high volume detection,initiates a control signal that causes the speed of gantry 104 andconveyor 102 to increase. When the high volume is no longer present, theuser can initiate a control signal that causes a reduction in the speedof the gantry 104 and conveyor 102. Thereafter, the method proceeds toand ends at step 508.

FIG. 6 depicts an embodiment of a method 600 used in accordance withaspects of this disclosure. The method 600 begins at step 602 andproceeds to step 604.

At step 604, the method 600 detects at least one bad detector. Asexplained above, detector is labeled a bad detector if informationreceived from the detector is not within the desired operatingparameters. Exemplary bad detector detection methods are presentedbelow. After detection of at least one bad detector, the method 600proceeds to step 606.

At step 606, the method compensates for a lack of resolution due to thebad detector(s). The compensation can be by increasing the rotationalspeed of gantry 104 and/or decreasing the speed of conveyor 102.Thereafter, the method proceeds to and ends at step 608.

FIG. 7 depicts an embodiment of a method 700 used in accordance withaspects of the invention. The order of the steps depicted in FIG. 7 (anddescribed below) is illustrative only. As such, the steps of method 700may be reformed in any suitable order or simultaneously, in accordancethe invention. Simultaneously, referring to FIGS. 1, 2, 3, and 7, themethod 700 begins at step 702 and proceeds to step 704.

At step 704, the method 700 initiates a self-check. In variousembodiments, the self-check 704 can be an automated diagnostic tool(e.g., detector signal checker 310 implemented in hardware and/orsoftware) that periodically tests for reception and/or integrity ofsignals received from detectors (e.g., detectors 200, 202, 204, 234,270, 282, 286, and/or 288) in the detector array 108. For example, invarious embodiments, after a preset number of scans or after anexpiration of a predetermined time, the scanning system 302 initiatesthe self-check 704.

In other embodiments, the self-check 704 is initiated when the system100 is initially turned on. In yet other embodiments, a user caninitiate the self-check 704 via user interface 322 and/or remotely viabaggage handling system 324.

After step 704, the method 700 proceeds to step 706. At step 706, themethod 700 determines whether detectors (e.g., detectors 200, 202, 204,234, 270, 282, 286, and/or 288) are bad (i.e., whether information isreceived from the detectors). The results of the determination can betransmitted to processor 314. If, at step 706 an affirmativedetermination is made (i.e., that there are bad detectors) each baddetector and its position in the detector array 108 is stored in memory(e.g., memory 330). Thereafter, the method 700 proceeds to step 708.

If, however a negative determination is made (i.e., that information isproperly received from the detectors (e.g., that none of the detectorsare faulty)) the method proceeds to and ends at step 714.

As indicated earlier, if an affirmative determination is made at step706, the method 700 proceeds to step 708. To increase the amount ofinformation gathered by the detector array 108, the amount of time thatan item (e.g., item 110 and/or item 112) is in the gantry is increased.This is can be accomplished by slowing the speed of the conveyor 102and/or increasing the rotational speed of gantry 104. The method 700determines, based in part upon the number and location of thefaulty/malfunctioning detector(s), a proper speed for the conveyor 102and/or rotational speed for the gantry 104 to obtain a desired imageresolution. The calculation can determine either the proper speed or anamount to adjust the current speed of the conveyor 102 and or gantry104.

The method 700 can use the results of the calculation(s) performed atstep 708 in various ways. For example, in various embodiments, theresults of the calculations performed at step 708 are transmittedtowards optional steps 716 to notify the baggage handling system (whichcan also include notification that the scanning system 300 needsmaintenance), 718 to notify the operator of system 100 (which can alsoinclude notification that the scanning system 300 needs maintenance),and/or 712 to assist in reconstruction of the image. After step 708, themethod proceeds towards step 710.

At step 710, the calculation in step 708 is used adjust the speed of theconveyor 102 and/or the gantry 104. The conveyor speed adjustment and/organtry speed adjustment can be made in a number of ways. For example, invarious embodiments, knowledge of the prior speed of the conveyor 102and/or gantry 104 can be used when the step 708 calculates the amount toadjust the speed of the conveyor 102 and/or gantry 104. Prior knowledgeof the speed of the conveyor 102 and/or the speed of the gantry 104 canbe obtained from memory 330. In addition, prior knowledge of the speedof the conveyor 102 and/or gantry 104 can be obtained in real-time fromthe conveyor control system 304, gantry motor controller 308, or otherspeed monitoring apparatus, that monitors the speed of the conveyor 102and gantry 104. In other embodiments, when the calculation is the properspeed of the conveyor 102 and/or gantry 104, adjustments are madewithout determining the difference between the current speed (of theconveyor 102 and/or gantry 104) and the desired speed (of the conveyor102 and/or gantry 104).

In one embodiment, after the speed of the conveyor 102 and/or gantry 104is adjusted in step 710, the method 700 proceeds to and ends at step714.

In other embodiments, after step 710 the method 700 proceeds to optionalstep 712. At step 712, an item is scanned, (using the adjusted conveyorspeed and/or gantry speed) and reconstructed using scanning system 300.Thereafter, the method 700 proceeds to and ends at step 714.

FIG. 8 depicts an exemplary method 800 for detecting at least onedetector in accordance with aspects of this disclosure. The method 800begins at step 801 and proceeds to step 802.

At step 802, the method calibrates the detectors in detector array 108to acquire values for each detector in detector array 108. Calibrationincludes scanning the air (i.e., scanning with nothing on the conveyor102) and using the acquired values in subsequent calculations. It ispresumed that for the values acquired at step 802 that the detectors arefunctioning within desired operating parameters. After scanning, themethod proceeds to step 804.

At step 804, the calibration values are stored in memory (e.g., memory330) for subsequent use. After certain condition(s), the method 800proceeds to step 806. Some exemplary conditions, which would cause themethod 800 to proceed to step 806, include, but are not limited to, aninitial start-up (i.e., “turning on”) of system 100, an expiration of apredetermined time, and/or a user request to proceed to step 806.

At step 806, the system 100 rescans for air (i.e., scans withoutanything on the conveyor 102) to acquire values for each of thedetectors in detector array 108. In various embodiments, the valuesacquired during rescanning may also be stored in memory (e.g., memory330). Thereafter, the method 800 proceeds to step 808.

At step 808, relationships are computed for each of the detectors indetector array 108 using the values acquired at step 802 and step 806.For example, in various embodiments, the relationships formed by (foreach detector) dividing the value acquired in step 802 by the valueacquired in step 806. After relationships are computed for all of thedetectors in detector array 108, the method 800 proceeds to step 810.

At step 810, the method 800 queries whether any of the relationshipsexceeds a predetermined threshold. The threshold can be predetermined ina number of ways. For example, the threshold can be predetermined inaccordance with resolution requirements and/or the application(s) (e.g.,medical imaging or security). For example, (in various embodiments) inmedical imaging a threshold deviation of about 1% is sufficient and forsecurity scanning a threshold deviation of about 10% is sufficient. Inyet other embodiments, the desired threshold deviation is dependent upondifferent locations in the gantry and/or detector array. If the query isanswered negatively, the method proceeds to step 818. At step 818, thesystem 100 enters a normal operation mode and is ready to scan items.Thereafter, the method proceeds to and ends at step 816.

If however, an affirmative determination is made at step 810 the method800 precedes to step 812. At step 812 each detector having arelationship that exceeds the threshold is flagged as a bad detector.The location of the bad detector(s) is stored in memory (e.g., memory330). After all of the bad detectors are flagged, the method 800proceeds to step 814.

At step 814, the method compensates for the bad detectors in thedetector array 108. Because at least one detector is bad, there may be aloss of resolution in a reconstructed image. To compensate for the baddetector image resolution is increased. For example, in variousembodiments, image resolution is increased by at least one of:decreasing the speed of the conveyor 102 to a predetermined speed;increasing the rotational speed of the gantry 104; or a combination ofincreasing the speed of the gantry 104 and decreasing the speed of theconveyor 102. Described below using FIGS. 9 and 10 is an exemplarymethod for correlating an acceptable conveyor speed with the baddetector(s). After compensation the method proceeds to step 818. At step818, the system 100 enters a normal operation mode and is ready to scanitems. Thereafter, the method proceeds to and ends at step 816.

In various embodiments, reducing the conveyor speed by a pre-determinedfactor (e.g., by about 25%) and/or increasing the gantry rotationalspeed by a pre-determined factor (e.g., increasing the gantry speedabove 120 R.P.M.s) compensates for bad detectors.

Different algorithms may be used to correlate the speed of the conveyor102 and/or speed of the gantry 104 with the number and location of thebad detector(s).

FIG. 9 depicts an embodiment of an area of influence 900 of an emitter(illustratively depicted as emitter 106) on a detector array(illustratively depicted as detector array 108). FIG. 9 depicts apositional relationship between emitter 106, the center of rotation 328,and detector 234 in detector array 108. For illustrative purposes, thearea of influence 900 is depicted as having a “fan shape.” However, itis appreciated that the area of influence can have other shapes (e.g., acone shape). Within the area of influence 900 are the center of rotation328 and detector array 108. For exemplary purposes, only one detector(i.e., detector 234) is depicted in detector array 108.

In FIG. 9 a distance “b” (see also lead-line 904) from a plane ofrotation of the center of rotation 328, as projected on an equivalentcylindrical detector 234 centered in the area of influence 900 of theemitter 106 and passing through the center of rotation 328 of the gantry104.

FIG. 9 also depicts an angle φ, which is an angle between the center ofrotation 328, and a projection of the detector 234 on a plane ofrotation of the center of rotation 328 and a central ray.

Using the relationship shown in FIG. 9 a formula can be created todetermine, for each bad detector (e.g., detector 234), a class ofcorresponding could be used to supplement the information missing frombad detector 234. A standard cylindrical detector is composed bydetectors having:−b _(max) <b<b _(max) and −φ_(max)<φ<φ_(max)  Equation (1)

where “b” and “φ” have already been defined above, b_(max) is the lengthof the detector in the direction of detector motion, −b_(max) is thelength of the detector in a direction of motion opposite to thedirection of motion for b_(max), φ_(max) is the length of a bend in thedetector array 108 in one direction, and −φ_(max) is the length of thein bend in the detector array 108 in a direction opposite to thedirection of φ_(max).

With an understanding of Equation (1) other formulas can be derived todetermine whether a given conveyor speed and/or gantry speed providesenough information (i.e., for reconstruction of an image having adequateresolution) to supplement missing information due to bad detectors. Forexample, one such equation is presented immediately below which producesall the possible corresponding detectors for a detector shown atcoordinates (φ, b) (illustratively detector 234):(φ_(equiv) ,b _(equiv))=(−φ,b+K*((2n−1)π−2φ)/cos(φ))  Equation (2)

where “b” “φ” have already been described above, K is the distancetraveled by the conveyor 102 during one rotation of the gantry 104, andn is the number of rotations of the gantry 104. Values that comply withEquation (1) are acceptable.

Computer software which utilizes Equation (1) and Equation (2) can beused to determine a conveyor speed and/or gantry speed for which verylittle (or no) information is missing given the detector(s) that arecurrently bad.

In addition, software simulations can be performed to determine whichconveyor speed provides sufficient information for reconstruction of animage having adequate resolution. For example, FIG. 10 depicts a method1000 which can be performed as a software simulation to predeterminegeometric ratio (i.e., relative speed) between the conveyor 102 andgantry 104 in accordance with aspects of this disclosure. The methodbegins at step 1002 and proceeds to step 1004. One way to simulatedetector failure is to mask the detector so that information will not bereceived from the detector. At step 1004, at least one detector in thedetector array 108 is masked. After detector masking, the method 1000proceeds to step 1006.

At step 1006, the method 1000 simulates an air scan while the conveyor102 is moving. The method 1000 analyzes the data obtained under theseconditions. At step 1006, verifies that at the present conveyor speedand gantry speed the data obtained is insufficient to reconstruct animage having the necessary resolution. Thereafter, the method 1000proceeds to step 1008.

At step 1008, the method 1000 annotates the conveyor speed (used in step1008) as V₀ and stores V₀ in memory. After step 1008, the method 1000proceeds to step 1010.

At step 1010, the simulated conveyor speed is reduced to 0. An air scanis performed and the data is analyzed for verification that the dataobtained is adequate to reconstruct the image with the necessaryresolution. After verification, the method 1000 proceeds to step 1012.

At step 1012 the conveyor speed used at 1010 is annotated at V₁.Thereafter, the method 1000 proceeds to step 1014.

At step 1014, an average of V0 and V1 is calculated and annotated as theaverage speed of the conveyor 102. The method 1000 simulates scanning asif the conveyor 102 were running at the average speed. The method 1000then determines whether the data acquired under these circumstances isadequate to reconstruct an image having adequate resolution. If themethod 1000 determines that the data acquired is adequate, the method1000 proceeds to step 1016.

At step 1016, the value stored as V₀ is replaced with the average speed.Thereafter, the method 1000 proceeds to step 1020.

At step 1020 the 1000 queries whether V₀ and V₁ have sufficientlyconverged (i.e., the difference between V₀ and V₁ is sufficientlysmall). If answered affirmatively, the method 1000 proceeds to and endsat step 222. If however, the query is answered negatively, the methodproceeds to step 1014.

If, at step 1014 the query is answered negatively, the method 1000proceeds to step 1018.

At step 1018, the value stored as V₁ is replaced with the average speed.Thereafter the method 1000 proceeds to step 1020.

Please note method 1000 correlates the gantry speed to the conveyorspeed. As such, it is appreciated that in various embodiments of method1000, the gantry speed can be increased (e.g., from 120 R.P.M.s to somehigher speed) and the steps performed in method 1000 (i.e., steps 1002through 1020) are performed at the higher gantry speed.

FIG. 11 depicts an exemplary graph 1100 in accordance with aspects ofthis disclosure. The graph 1100 contains data lines demonstrating fourconditions. The conditions are as follows: a pitch of 1.5000 and no baddetectors (referred to hereinafter as “condition 1106”); a pitch of1.5000 with bad detectors and naïve correction is used to compensate forthe bad detectors (referred to hereinafter as “condition 1108”); a pitchof 0.7500 with bad detectors and naïve correction is used to compensatefor the bad detectors (referred to hereinafter as “condition 1110”); anda pitch of 0.7500 with bad detectors and advanced correction is used tocompensate for the bad detectors (referred to hereinafter as “condition1112”). “Naïve” correction, as used herein, indicates the use ofapproximation techniques to determine the information contained in a baddetector(s).

Cross-sectional image slices for conditions 1106, 1108, 1110, and 1112are depicted in FIGS. 14-17, respectively. Note that FIGS. 14-17 aredepicted as having a resolution of 1024×1024. However, that resolutionis for illustrative purposes only and not intended in any way to limitthe scope of the invention.

FIG. 14 depicts an image 1400 scanned under condition 1106 (i.e., havinga pitch of 1.5000 and no bad sectors). The image 1400 contains anextracted profile 1406 viewed at the illustrative resolution 1402 of1024×1024. Image 1400 also includes contrast chart 1404 that shows,within an arbitrary scale factor, the numeric meaning of the differentshades of grey, which is proportional to the X-ray absorption propertiesof the material being imaged.

FIG. 15 depicts an image 1500 scanned under condition 1108 (i.e., havinga pitch of 1.5000, bad sectors, and corrected using naïve correction).The image 1500 contains an extracted profile 1504 viewed at theillustrative resolution 1402 of 1024×1024. A comparison of profile 1406with profile 1504 shows the disparity between the clarity of profiles1406 and 1504. When using naïve correction, the resolution of theperiphery of profile 1504 is visibly lower than the resolution of theperiphery of profile 1406. Image 1500 also includes contrast chart 1502that shows within an arbitrary scale factor, the numeric meaning of thedifferent shades of grey, which is proportional to the X-ray absorptionproperties of the material being imaged.

FIG. 16 depicts an image 1600 scanned under condition 1110 (i.e., havinga pitch of 0.7500 and bad sectors). The image 1600 contains an extractedprofile 1604 viewed at the illustrative resolution 1402 of 1024×1024. Acomparison of profile 1406 with profile 1604 shows the disparity betweenthe clarity of profiles 1406 and 1604. When using naïve correction, theresolution of the periphery of profile 1604 is visibly lower than theresolution of the periphery of profile 1406. Image 1600 also includescontrast chart 1602 that shows within an arbitrary scale factor, thenumeric meaning of the different shades of grey, which is proportionalto the X-ray absorption properties of the material being imaged.

In contrast to FIGS. 15 and 16, FIG. 17 depicts an image 1700 scannedunder condition 1112 (i.e., having a pitch of 0.7500, bad sectors, andcorrected using advanced correction). The image 1700 contains anextracted profile 1704 viewed at the illustrative resolution 1402 of1024×1024. A comparison of profile 1406 with profile 1704 shows novisible disparity between the clarity of profiles 1406 and 1704. Image1700 also includes contrast chart 1702 that shows within an arbitraryscale factor, the numeric meaning of the different shades of grey, whichis proportional to the X-ray absorption properties of the material beingimaged.

Returning to graph 1100 in FIG. 11, the X-axis 1104 spans from 0 toabout 2 lines per pixel. The Y-axis 1102 demarks a contrast from about 0to 1. Note that in graph 1100, condition 1106 is the condition uponwhich conditions 1108, 1110, and 1112 would ideally replicate. Inconditions 1108 and 1110 which both use naïve correction there is asignificant drop in contrast at lower resolutions. However, condition1112, which uses advanced correction to compensate for bad detectors,appears to mimic condition 1106 that has no bad detectors.

FIG. 12 depicts a close up view of a portion 1200 of the exemplary firstgraph 1100 depicted in FIG. 11. In portion 1200, the X-axis 1104 spansfrom 0 to about 0.2 lines per pixel.

FIG. 13 depicts a graph 1300 of the CT value corresponding with the edgeof an object created using first modulation transfer function (“MTF”).The graph 1300 shows the value of the MTF on the “Y” axis 1302 (whereperfect contrast corresponds to a value of the MTF of 1) as a functionof the special resolution, indicated on the “X” axis 1304 havingdemarcations to delineate line-pairs per pixel.

To clearly understand the data shown in graph 1300, a reader isencouraged to simultaneously view FIGS. 14-17. The X-axis 1304 representthe pixel number, while the Y-axis 1302 represents the CT value. In anideal case, a jump from the CT value of 1 to the CT value of 0 would beas stark as possible. Profile 1306 is the profile extracted from FIG.14, and corresponds to a normal operation state of the scanner. Profile1308 is the profile extracted from FIG. 15, and corresponds to thescanner operating with bad detectors, and using the naïve correction.Profile 1310 is the profile extracted from FIG. 16, and corresponds tothe scanner operating with bad detectors, but running at half the pitch,and using the naïve correction. Profile 1312 is the profile extractedfrom FIG. 17, and corresponds to the scanner operating with baddetectors, running at half the normal pitch and using the advancedcorrection. Profile 1312 is practically undistinguishable from profile1306, while profiles 1308 and 1310 show obvious loss of resolution.

FIG. 18 depicts a high-level block diagram of a computer architecturefor performing an embodiment of the invention. FIG. 18 depicts ageneral-purpose computer 1800 suitable for use in performing the methodsof FIGS. 4-8 and 10; and Equation (1) and Equation (2) described abovewith respect to FIG. 9.

The general-purpose computer of FIG. 18 includes a processor 1810 aswell as a memory 1804 for storing control programs and the like. Theprocessor 1810 cooperates with conventional support circuitry 1808 suchas power supplies, clock circuits, cache memory and the like as well ascircuits that assist in executing the software routines 1806 and a CTefficiency module 1812 stored in the memory 1804. As such, it iscontemplated that some of the process steps discussed herein as softwareprocesses may be loaded from a storage device (e.g., an optical drive,floppy drive, disk drive, etc.) and implemented within the memory 1804and operated by the processor 1810. Thus, various steps and methods ofthe present invention can be stored on a computer readable medium. Thegeneral-purpose computer 1800 also contains input-output circuitry 1802that forms an interface between the various functional elementscommunicating with the general-purpose computer 1800. For example, inthe embodiment one of FIG. 18, the general-purpose computer 1800communicates with user interface 322 and/or baggage handling system 324(shown in FIG. 3). The processor 1810 interprets inputs received fromthe user interface 322 and/or baggage handling system 324 and, inresponse thereto; the processor 1810 forwards the instructions theseinstructions accordingly (e.g., to the detector signal checker 310, theconveyor motor controller 320, and/or the gantry motor controller 308).The processor 1810 uses the information acquired from the detectorsignal checker 310 to instruct, via the CT efficiency module 1812, theconveyor motor controller 320 to adjust the speed of the conveyor 102(if needed) and/or adjust the speed of the gantry 104; and reconstructan image of an item (if an item is present). In addition, the processor1810, via CT efficiency module 1812, increases the speed of the gantry104 and the speed of the conveyor 102 for faster scanning as explainedabove.

Although FIG. 18 depicts a general-purpose computer that is programmedto perform various control functions in accordance with the presentinvention, the term computer is not limited to just those integratedcircuits referred to in the art as computers, but broadly refers tocomputers, processors, microcontrollers, microcomputers, programmablelogic controllers, application specific integrated circuits, and otherprogrammable circuits, and these terms are used interchangeably herein.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the appended claims, and may include other examples thatoccur to those skilled in the art. Such other examples are intended tobe within the scope of the claims if they have structural elements thatdo not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

In addition, it is also within the scope of the material disclosedherein that a computer-readable medium having stored thereon a pluralityof instructions, the plurality of instructions including instructionswhich, when executed by a processor, cause the processor to perform thesteps as depicted and described above (e.g., in FIGS. 4-8 and 10).

1. A method comprising: detecting at least one faulty X-ray detectorsignal in a plurality of X-ray detector signals, wherein each X-raydetector signal in said plurality has a detector associated therewith;and adjusting at least one of a conveyor speed and a gantry rotationalspeed in accordance with said detection.
 2. The method of claim 1wherein said adjusting further comprises: calculating at least one ofdesired conveyor speed and a desired gantry speed in accordance with adetector position for said at least one faulty X-ray detector signal. 3.The method of claim 2 further comprising transmitting said calculationto at least one of a remote baggage handling system, an imagereconstruction module, a local user interface, and a conveyor motorcontroller.
 4. The method of claim 1 wherein said adjusting furthercomprises: calculating a difference between a reference conveyor speedand a desired conveyor speed in accordance with a detector position forsaid at least one faulty X-ray detector signal.
 5. The method of claim 1further comprising: performing primary gain scans at a first time;storing primary data associated with said primary gain scans at saidfirst time; performing secondary gain scans at a second time; storingsecondary data associated with said secondary gain scans at said secondtime; computing, for each said detector, a relationship between saidprimary data and said secondary data; and flagging said detector as abad detector when said relationship exceeds a threshold.
 6. The methodof claim 1 wherein said adjusting of said conveyor speed increases anumber of computed tomography (“CT”) slices.
 7. The method of claim 1wherein said adjusting of said gantry rotational speed increases a rateat which computed tomography (“CT”) slices are acquired.
 8. A systemcomprising: a gantry; an X-ray emitter configured to emit X-rays withinsaid gantry; a detector array within said gantry and adapted to detectsaid X-rays wherein said detector array has a plurality of detectors; aconveyor configured to move objects through said gantry; a subsystemconfigured to check integrity of said plurality of detectors; and asecond subsystem configured to adjust at least one of a speed of saidconveyor and a speed of said gantry in accordance with said integritycheck to achieve a desired resolution.